Radio phase modulator



Oct. 10, 1950 w. SMITH RADIO PHASE MODULATOR Filed Aug. 22, 1944 PHASE MODULATOR I 5| F IE IS WILLIAM L SMITH T anw 5mm 2. SD '0 6x m I H 9 0 L 5M0 P 6 6 a I n5 F mm s a m T E LE o A... 5M A rm N .rM omw 05 I r I 3 a M 5 M 0 5 4 um I G mve a w H a F W Fatentecl 6d. if), 1950 i- UNITED STATES ATENT OFFICE 4 Claims.

This invention relates to apparatus forv phase modulating an. alternating. potential.

:Among the several objects of my invention are:

To provide a means for phase modulating'an alternating electric potential;

To provide a means for phase modulation with-out substantial change in the amplitude of the modulated wave;

To provide a means for phase modulation that does not require. the use of frequency multipliers followed by heterodyning to increase the percentage of frequency shift, with the increase in power consumption and complexity of the circuit, and reduced. stability of the mean frequency, that are often present when'more complicated systems are employed;

To provide a means for. repeated increases in phase deviation to obtain a desired degree of. phase modulation.

In the drawings:

Fig. l is a diagram of an elementary circuit in. which phase deviations will be produced;

Figs. 2 and 3 show the vectors of. potential across the resistance and the reactancein. Fig. 1, respectively, as the value of the resistance is changed;

Fig. 4 is a diagram of an'elementary circuit wherein changes of potential as shown inzFig. 5 will result from variations of the value of the: resistance in Fig. 4.

Fig. 6 is a diagram of g a vacuum tube :connected to present a reactive impedance;

Fig. 7 is a diagram of a vacuum tube. connected to present a resistive impedance;

Fig. 8 isa circuit equivalent to Fig. 4 whereinthe vacuum tube function has a variable resistance;

Fig. 9 is a block diagram of the circuit in Fig. 8;

Fig. 10 is a block diagram of a system wherein a resistance is used in connection with a'vacuum tube acting as a variable reactance;

Fig. 11 is a block diagram wherein vacuum tubes function as both a resistance and a re-- actance and are simultaneously varied to give augmented phase shift;

Fig. 12 is a block diagram of an elementary circuit for producing phase variations as indi-' cated in Fig. 13;

Fig. 14 isablock diagram showing the application of phase deviating potentials to cascaded. phase modulators'toeifect the increased. phase deviations shown inFig. 15';

"Fig. 16 is a block diagramshowing the application of phase deviating. potentials tora plurality of cascaded phase modulatorsto' effect the amended AprilBO, 1928; 370 O. G. 757) increased phase deviations shown in Fig. 17. Hereinafter the terms reactance tube and resistance tube will be used for the sake of brevity to denote vacuum tubes and circuit components connected therewith to cause the tubes to exhibit the types of impedance respectively mentioned. Since at high frequency even'a re sistance shows inductance and capacity effects it is not incorrect to consider the impedance of the resistance as havinga mean value.

One of the problems in phase modulating an i alternating potential is to obtain sufficient phase deviation without excessive amplitude modulation. The prior art known to me has found it necessary; in phase modulating systems to follow the phase modulator with frequency multiplication and heterodyning, but the apparatus required greatly increases the power consumption; reduces the stability of'the mean frequency and adds to the complexity of the circuits. The present invention provides for adequate phase modulation without these undesirable features. Fig. 1 depicts'an elementary circuit for phase modulation wherein source I6 of alternating potential is connected in series with a capacitor I! and a resistor 18, the output of the source l6 being a pure wave form of constant frequency. and amplitude.

resistor IE! will change from zero to a value equal to the applied potential as shown in Fig. 2 and the potential across the capacitor l1 will vary from a value equal to the applied potential to zero, as shown in Fig. 3. If an inductance be substituted for capacitor ll the direction of departure from the phase of the applied potential will be reversed. If the resistor id be held constant and the value of the reactance represented by capacitor ll be varied, the direction of rotation of the potential vectors will be reversed. In

all casesthe curve generated by the tip" of the potential vector is a semi-circle with its center located at apoint equivalent to one-half'the applied potential and-with its radius equalto one-half the applied potential.

Ifnow, as in Fig. 4, the source of potential [9 be provided with a potential mid-point, as by means of a center tap on its windings'or other- I wise,.then the potential 20rexisting between such midepoint and, the junction between reactance I! and resistance [8 will vary froma value of. minus one-half the applied potential to'a value of plus one-half the same, as shown inFig. 5, when'the value of the resistance l8"is varied from zero to infinity. If reactance lljin Figl 4is aninduct- When the value of resistor I8 isvaried from zero to infinity the potential across ance, instead of a capacitance as shown, the direction of the departure from the phase of the applied potential will be reversed. If resistance I8 be held constant and the value of reactance I! be varied the direction of rotation of the potential vector will be reversed. The curve generated by the tip of the potential vector will be in all cases a semi-circle with its center at zero and a radius equal to one-half the applied potential. Thus as the value of resistance I8 or reactance I1 is varied the phase of potential 20 relative to the phase of source I9 is varied, but the amplitude of potential 29 remains constant at a value equal to one-half that of source I9.

The mean phase of potential 20 relative to that of source I9 is 90, the sign of the angle depending upon the type of reactance employed and the details of the circuit arrangement. Varying the absolute value of reactance I! or of resistance I8, or of both, will change the actual phase of potential 20 with a respect to that of the source I9 from zero to 180, the sign of the angle depending upon the type of reactance employed and the details of the circuit arrangement, and the actual phase of potential 20 relative to its mean value will be varied plus or minus 90. Throughout these variations in phase, the amplitude of potential 28 will remain unchanged at a value equal to one-half that of the source I9.

As is well known in the art, a multi-electrode vacuum tube may be connected with other circuit elements in such a manner that the impedance existing between two points in the circuit is substantially equivalent to a reactance or a resistance or a mixture of both, the absolute value of which depends upon the relative potential applied to one or more of the electrodes of the tube. This is illustrated in Figs. 6 and '7. In the former of these figures, a vacuum tube 2| has an anode resistor 22, a grid resistor 23 a capacitance 24 connected between anode and grid, and a resistor 25 connected between grid and cathode, which cause tube 2| to exhibit a reactive impedance between the point 26 and ground, the absolute value of this impedance depending upon the relative potential applied to the grid through resistor 23. In Fig. 7 the tube 21 is associated with an anode resistor 28 and shows resistive impedance lbetween point 30 and ground having a value dependent upon a relative potential applied to grid 29.

It is evident that if reactance I! or resistance I8, or both, be simulated by a vacuum tube, or tubes as the case may be, connected as in one or both of Figs fi and 7, respectively, the relative phase of potential 20 may be varied by a quantity approaching 90 from its mean phase by proper variation of the relative potential applied to the grid of the respective tube or tubes. This is shown schematically in Fig. 8 where an alternating potential of constant frequency and amplitude is fed from source 3| to the primary 32 of transformer 33, the secondary 34 of which is tuned to resonance with source 3| by capacitors 35 and 36 Which are adjusted to have equal capacities. In series with the anode-cathode circuit of tube 31 Which includes grid-bias resistor 38 is a capacitor 39. The circuit components associated with tube 3'! are such that this tube exhibits resistive impedance, the absolute value of which depends upon the relative potential applied to grid 48 by source 4i. With the impedance of capacitor 39 adjusted to be equal to the mean value of the impedance of tube 31, the output taken from leads 42 and 43, connected to the said potential mid-point and a ground, respectively, will be phase modulated exactly as in the equivalent circuit of Fig. 4. The anode supply is connected to leads 44.

To simplify the drawings in further discussion and to make clear the significance of the following figures, the system of Fig. 8 is shown in block form in Fig. 9 wherein the reference characters designate the same elements as in Fig. 8 except that transformer 33 and capacitors 35 and 36 are as a group designated by the numeral 45. Fig. 10 shows a system that is in general similar to that of Fig. 9 except that a resistor 46 is substituted for the resistance tube 31 and a reactance tube 41 is substituted for the capacitor 39.

Fig. 11 depicts a further development of the principles of my invention wherein a reactance tube 48 and a resistance tube 49 are connected in series and the values of the respective impedances thereof are varied by the potential applied from source 4|. It will, of course, be understood that the variations in the impedances of tubes 48 and 49 will be such as to produce an additive-phase deviation. It will be further understood that the networks designated by 48 and 49 will be equivalent to those shown in Figs. 6 and 7, respectively.

My present invention may be expanded to produce successive phase deviations that will result in a final phase modulation of any desired practicable magnitude. This is done by applying a phase modulating potential seriatim to cascaded phase modulators, in the respectively proper phase relation at each phase modulator to increase the deviation from the mean frequency. The modulators used for this purpose are, preferably, but not necessarily, of the type above described. This aspect of my invention is illustrated in general by the block diagrams of Figs. 12 and 14. In Fig. 12 an alternating potential of constant amplitude and frequency from source 50 is applied to a phase modulator 5|, which may be any suitable system such as one of those above described, wherein it is combined with a modulating potential from the source 52 and the output delivered to load 53 will have superimposed thereon variations of phase whereof the direc-- tion and magnitude are proportional to the instantaneous potential of the source 52. The phase deviations from the mean phase 54 in Fig. 13 are represented by the vectors '55 and 56.

If a greater degree of phase modulation is necessary or desirable, additional phase modulators 51 may be cascaded with modulator 5I ahead of the load 53 and the modulating potential from source 52 applied to such additional phase modulators 51 in the proper phase to result in cumulative phase deviation. The efiect of adding the phase modulator 51 is shown graphically in Fig. 15 wherein the vector 56 represents the phase deviation produced in modulator 5| and the vector 58 the additional modulation impressed in modulator 51. While only two phase modulators in cascade are shown it is obvious that the process may be continued by adding a plurality of modulators in cascade ahead of load 53 until a total final deviation of phase having the desired magnitude is attained as shown in block diagram in Fig. 16 and graphically in Fig. 17.

Fig. 16 is Fig. 14 expanded to produce a plurality of successive phase deviations that will result in a final phase modulation of any desired magnitude. The blocks 59 and 6| are additional phase modulators; In the graphic Fig. 17, the

angle included between vectors 60 and 60 represents the total phase deviation produced in modulators 5|, 5'! and 59, the portions of such angle lying between vector 58 and vector 60 and between vector 58 and vector 60' representing that portion of the total modulation contributed by modulator 59. The angle included between vectors 62 and 62' represents the total phase deviation produced in modulators 5|, 51, and 6!.

Block 50 is a source of unmodulated alternating current, or a wave source, such as a crystalcontrolled oscillator. Blocks 5!, 51, 59 and El are phase modulators of the type shown in the cited Patents Nos. 1,950,406, 2,045,107 and 2,160,528. 'Item 52 is a source modulating signal, such as a microphone, record pick-up or television camera tube, including means to impress upon each of said phase modulators the said modulating signals in proper relation to augment the phase modulation present in the output of the respectively preceding phase modulator, and may include an amplifier. Item 53 is a load or utilization circuit, possibly including amplifiers, frequency multipliers, antenna, etc.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of-any royalties thereon or therefor.

I claim:

1. A phase modulation system for a source of oscillations of relatively fixed frequency comprising a plurality of modulation networks connected in cascade, each network comprising a first electron tube operated so that its anode-cathode path constitutes a resistance connected in series with a second electron tube operated so that its anode-cathode path constitutes a capacitive reactance, the first of said plurality of networks being connected to said source of oscillations and the input of each succeeding network being connected to the output of the preceding network and means to impress upon each of the electron tubes in each of the networks a modulating potential whereby the output of the final network has substantially the same mean frequency as the source of oscillations and phase deviation substantially equal to the sum of the deviations produced in said individual networks.

2. A phase modulation system for a source of oscillations of relatively fixed frequency wherein the phase deviation at the output of the system is essentially equal to the sum of the deviations produced by the individual stages of the system comprising a source of relatively fixed oscillations, a plurality of modulation networks connected in cascade, a first electron tube function-' ing as an effective resistive impedance, a second electron tube functioning as a capacitive reactance; each of said electron tubes'containing at least an anode, cathode and control grid; said first and second tubes being connected in series to comprise each of the plurality of networks, said tubes in the first of said networks being connected in series across the above-mentioned source of oscillations, and means to impress on the control grids of each of said tubes a varying modulating potential whereby the output of the system is substantially equal to the sum of the deviations produced in said networks and at substantially the same mean frequency as the source of oscillations.

3. A phase modulating system comprising a first phase modulating network, means to impress on said network an alternating potential of substantially constant amplitude and frequency, said'first network comprising a first and a second electron tube connected in series, said first electron tube being operated so that its anode-cathode path constitutes a resistance and said second electron tube being operated so that its anode-cathode path constitutes a reactance, a plurality of phase modulating networks similar to said first network and connected in cascade therewith, the input of each network having impressed thereon the output of the respectively preceding network, and means to impress upon each of said networks a varying modulating potential in proper relation to add to the phase modulation produced therein the phase modulation present in the output of the respectively preceding network, whereby the output of the final network has substantially the same mean frequency as said alternating potential and a phase deviation substantially equal to the sum of the deviations produced in all of said networks.

4. A phase modulating system comprising a first phase modulating network, meansto impress on said network an alternating potential of substantially constant amplitude and frequency, said first network comprising a first and a second electron tube, said first electron tube being operated so that its anode-cathode path constitutes a resistance and said second electron tube being operated so that its anode-cathode path constitutes a reactance, a second phase modulating network similar to said first network and connected in cascade thereto, a varying modulating potential, and means to impress upon each of said networks the modulating potential, whereby the output of the second network has substantially the same'mean frequency as said alternating potential and a phase deviation substantially equal to the sum of the deviations produced in each of said networks.

WILLIAM L. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Stodola Mar. 2, 1948 

